Organophosphorus nickel complexes and preparation thereof

ABSTRACT

The preparation and use of bis(μ-diphenylphosphido)tris(triethylphosphine)dinickel and tris(triethylphosphine)(triphenylphosphine)nickel is disclosed.

This invention relates to organo-nickel complexes. In another aspectthis invention relates to organophosphorus nickel complexes and theiruse.

Methods are known in the art for the dimerization of olefinichydrocarbons in the presence of a catalyst system containing a nickelcomplex. Dimerization of propylene and other lower monoolefins continuesto be of interest in the synthesis of monomers for additionpolymerization, as intermediates in alcohol production by the oxoprocess, and as intermediates in the manufacture of plasticizers, lubeadditives, monomers for condensation polymerization, detergent basematerials, improved motor fuel and the like. This continuing interesthas established a need in the art for improved nickel complexdimerization catalysts. The extent of the dimerization, as well asstability of the resulting catalyst, is greatly dependent upon thecharacter of the components employed to produce the catalyst system. Ingeneral, substantial variations in resulting dimer product types,catalyst stability, and olefin conversion are encountered when thecharacter of the catalyst complex is varied.

It is an object of the present invention to provide a novelorganophosphorus nickel complex which can be employed in theoligomerization of monoolefins or conjugated dienes.

A further object of the present invention is to provide another novelorganophosphorus nickel complex which can be employed to prepare thepreviously-mentioned nickel complex.

A further object of the present invention is to provide processes forpreparing both nickel complexes.

A still further object is to provide processes for oligomerizingmonoolefins or conjugated dienes employing said first-mentioned novelorganophosphorus nickel complex.

The first-mentioned novel organophosphorus complex of this invention isbis(μ-diphenylphosphido)tris(triethylphosphine)dinickel, hereinafterreferred to for convenience as Ni₂ (μ-PPh₂)₂ (PEt₃)₃.

The second-mentioned novel organophosphorus complex of this invention istris(triethylphosphine)(triphenylphosphine)nickel(O), hereinafterreferred to for convenience as Ni(PEt₃)₃ (PPh₃).

The organophosphorus nickel complexes of this invention, like many ofthe compounds employed in preparing them, are sensitive to oxygen and/orwater to varying degrees. Therefore the preparation and use of thesecomplexes should be conducted under an inert atmosphere, for example ina recirculating-atmosphere drybox providing an inert atmosphere.

One method of preparing Ni(PEt₃)₃ (PPh₃) according to this inventioninvolves reacting suitable amounts oftetrakis(triethylphosphine)nickel(O) and triphenylphosphine in asuitable diluent under reaction conditions that will yield saidNi(PEt₃)₃ (PPh₃). While any suitable temperature can be employed, ingeneral the temperature will be in the range of about -50° to about 100°C. Preferably the reaction temperature is in the range of about -20° toabout 50° C. Any suitable molar ratio of triphenylphosphine to Ni(PEt₃)₄can be employed, but in general this ratio will be in the range of about0.1:1 to about 1:0.1, and preferably in the range of about 0.5:1 toabout 1:0.5. Any pressure is satisfactory that will essentially maintainthe diluent in the liquid phase at the reaction temperature. In generalthe pressure will be in the range of about 5 to about 1000 psia, andatmospheric pressure is preferred. Any diluent can be employed that doesnot prevent the formation of Ni(PEt₃)₃ (PPh₃). Suitable diluentsinclude, for example, unsubstituted ethers, aromatic hydrocarbons,aliphatic hydrocarbons, and mixtures of any two or more thereof. Typicalexamples of diluents include diethyl ether, p-dioxane, tetrahydrofuran,benzene, toluene, pentane, hexane, octane, and mixtures of two or morethereof. Any suitable time for reaction can be employed, but of courseit will be dependent upon the conditions employed. The reaction time isgenerally in the range of about 1 minute to about 10 hours, andpreferably in the range of about 0.1 hour to about 2 hours.

The Ni(PEt₃)₃ (PPh₃) can then be recovered and purified using techniquesconventionally employed by those skilled in the art for recovering andpurifying products contained in a diluent, i.e., precipitation,filtration and washing; or evaporation in vacuo, separation ofimpurities by chromatography, and recrystallization.

The product Ni(PEt₃)₃ (PPh₃) in a suitable diluent is converted to thenovel complex Ni₂ (μ-PPh₂)₂ (PEt₃)₃. Any suitable temperature can beemployed. Generally, temperatures in the range of about 25° to about175° C are satisfactory. It is now preferred that temperatures be in therange of about 60° to about 130° C. Any diluent can be employed thatdoes not prevent the formation of the Ni₂ (μ-PPh₂)₂ (PEt₃)₃. Suitablediluents include for example, unsubstituted ethers, aromatichydrocarbons, aliphatic hydrocarbons, and mixtures of any two or morethereof. Typical examples of such diluents include diethyl ether,p-dioxane, tetrahydrofuran, benzene, toluene, pentane, hexane, octaneand mixtures of two or more thereof. The preferred diluents arealiphatic hydrocarbons containing 5 to 10 carbon atoms. Any pressure issatisfactory that will essentially maintain the diluent in the liquidphase at the reaction temperature. In general the pressure will be inthe range of about 5 to about 1000 psia, and atmospheric pressure ispreferred. Any suitable time for the reaction can be employed, but ofcourse it will be dependent upon the conditions employed and the yieldsought. The reaction time will generally be in the range of about 0.1hour to about 100 hours, preferably in the range of about 1 to about 6hours.

Another process for preparing Ni₂ (μ-PPh₂)₂ (PEt₃)₃ comprises reacting amixture of suitable amounts of Ni(PEt₃)₄ andpentafluorophenyldiphenylphosphine in a suitable diluent. Again thereaction pressure is any pressure that will essentially maintain thediluent in the liquid phase at the reaction temperature. In general thepressure will be in the range of about 5 to about 1000 psia, andatmospheric pressure is preferred. Any suitable reaction temperature canbe employed. Generally temperatures in the range of about -10° to about150° C, preferably in the range of about 0° to about 60° aresatisfactory. Any diluent can be employed that does not prevent theformation of Ni₂ (μ-PPh₂)₂ (PEt₃)₃. Suitable diluents include thoseexamples set forth in the process described in the preceding paragraph.Particularly preferred diluents are aliphatic unsubstituted ethers. Themolar ratio of pentafluorophenyldiphenylphosphine to Ni(PEt₃)₄ isgenerally in the range of about 0.1:1 to 1:0.1 and preferably is about0.5:1 to 1:0.5. Again the time for this reaction will of course bedependent upon the conditions employed and the yield sought. Thereaction time is generally in the range of about 0.1 hour to about 100hours, preferably in the range of about 1 to about 6 hours.

Still another process for preparing Ni₂ (μ-PPh₂)₂ (PEt₃)₃ comprisesreacting suitable amounts oftrans-dichlorobis(triethylphosphine)nickel(II) with lithiumdiphenylphosphide etherate in a suitable diluent under suitable reactionconditions to yield a reaction product which is then reacted in asuitable diluent with a suitable amount of Ni(PEt₃)₄. Generally the moleratio of lithium diphenylphosphide etherate totrans-dichlorobis(triethylphosphine)nickel(II) is in the range of about1.5:1 to about 2.5/1. preferably about 2:1. Any suitable mole ratio ofNi(PEt₃)₄ to trans-dichlorobis(triethylphosphine)nickel(II) can beemployed but, in general this ratio will be in the range of about 0.5:1to about 10:1, preferably about 1:1 to 1.5:1. While any suitablereaction temperature can be employed, in general the reactions areconducted in the temperature range of about -50° to about 150° C,preferably about 0° to about 25° C. Any diluent can be employed thatdoes not prevent the formation of Ni₂ (μ-PPh₂)₂ (PEt₃)₃. The preferreddiluents are ethers or ether-hydrocarbon admixtures. Unsubstitutedaliphatic ethers or combination thereof with aliphatic hydrocarbons areespecially preferred. Typical examples include diethyl ether, p-dioxane,tetrahydrofuran, or combinations of such ethers with hydrocarbons suchas benzene, toluene, pentane, hexane and octane. Again in this processthe pressure is any pressure that will essentially maintain the diluentin the liquid phase at the reaction temperature. In general the pressurewill be in the range of about 5 to about 1000 psia and atmosphericpressure is preferred. The reaction time will of course depend upon theconditions employed and the yield sought; however, the reaction time isgenerally in the range of about 0.1 hour to about 100 hours, preferablyin the range of about 0.5 to about 6 hours.

The product, Ni₂ (μ-PPh₂)₂ (PEt₃)₃, produced by any of the threeprocesses just described can be recovered and purified using techniquesconventionally employed by those skilled in the art. For this reason itis convenient that a diluent be selected in which the dinickel complexis relatively insoluble at a temperature on the order of about -20° toabout -80° C. Alternatively it is convenient to employ a diluent that issufficiently volatile that the dinickel complex can be isolated byevaporating the reaction mixture in vacuo.

The novel compound Ni₂ (μ-PPh₂)₂ (PEt₃)₃ is useful in theoligomerization of monoolefins or conjugated dienes.

In accordance with the process for oligomerizing monoolefins, a catalystsystem is employed comprising Ni₂ (μ-PPh₂)₂ (PEt₃)₃ and at least oneorganoaluminum compound represented by the formula R_(n) AlX_(3-n),wherein each R is a hydrocarbyl radical having from 1 to 20 carbonatoms; each X is a halogen; and n is 1, 1.5, or 2.

Some specific examples of organoaluminum components of the catalystsystem are: methylaluminum dichloride, dimethylaluminum chloride,diethylaluminum bromide, ethylaluminum dibromide, vinylaluminumdiiodide, dibutylaluminum chloride, phenylaluminum dibromide,dibenzylaluminum chloride, 4-tolylaluminum dichloride, dodecylaluminumdibromide, methylaluminum sesquichloride, and the like mixtures thereof.Presently preferred aluminum compounds are organoaluminum halidesparticularly those containing hydrocarbon radicals having 1 to 6carbons, such as methylaluminum sesquichloride.

The catalyst components can be combined in any suitable proportions.Generally they are combined in proportions in a range of 0.5:1 to about20:1 moles of an organoaluminum halide per mole of nickel complex.Catalyst poisons in the system can be scavenged by employing evengreater proportions of the organoaluminum compound.

The catalyst system is prepared by combining the first and secondcomponents of the catalyst under suitable conditions of time andtemperature which permit the active catalyst to be formed. The twocomponents of the catalyst system can be mixed under any suitabletemperature. Generally the temperature at which the catalyst is preparedis in the range of about -80° to about 100° C for a period of timeranging from a few seconds up to several hours in the presence of adiluent in which both of the two components are at least partiallysoluble. Any diluent is suitable that is an inert liquid under thereaction conditions. Examples of suitable solvents or diluents arebenzene, cyclohexane, chlorobenzene, methylene chloride, ethylenechloride, and the like. However, halogenated diluents are preferred. Theforming of the catalyst system by admixing the two components isgenerally carried out in an inert atmosphere and in the substantialabsence of air or moisture. After the catalyst system is formed, it neednot be isolated but can be added directly to the reaction zone as asolution or suspension in its preparation medium. If desired, thecomponents used to form the catalyst system can be separately added, inany order, to the reaction zone either in the presence or absence of thefeed olefin.

Any suitable monoolefin can be oligomerized employing the just-describedcatalyst system. Examples of suitable monoolefins include, for example,ethylene, propylene, butene-1, butene-2, pentene-1,pentene-2,cyclopentene, cyclohexene, 3,4,5-trimethylcyclohexene,3-methylbutene-1, cycloheptene, hexene-2, heptene-1, cyclooctene,4,4-dimethylheptene-2, decene-1, dodecene-1, and the like, and mixturesof any two or more thereof. The preferred monoolefins are those havingfrom 2 to 12 carbon atoms and no branching on a doubly bonded carbon.Especially preferred at the present time is propylene.

The oligomerization of the monoolefin or mixture of monoolefins can takeplace at any suitable temperature. Generally the temperature is withinthe range of -80° to about 200° C, and preferably within the range of-10° to about 50° C. The reaction is carried out with the diluent in theliquid phase. Also any suitable pressure can be employed. Normally, itis desirable to carry out the dimerization reaction under pressuresranging from about 0 psig up to about 2000 psig and preferably 20-50psig. The oligomerization can be carried out in the presence of adiluent such as that used for the catalyst preparation if desired. Thetime of contact of the olefin with the catalyst for the oligomerizationof the olefin will vary depending upon the desired degree of conversionbut generally will be within the range from about 0.1 minute to about 20hours, preferably 5 to 120 minutes. The proportion of nickel complex toolefin feed in the reaction zone will generally be within the range ofabout 0.00001 to about 0.1 mole of nickel complex per mole of olefinfeed.

Any conventional contacting technique can be utilized for the olefinoligomerization and batchwise or continuous operations can be utilized.After the desired degree of conversion of the olefin to the dimer, theproducts so formed can be separated and isolated by conventional meanssuch as by fractionation, crystallization, adsorption, and the like. Theunconverted feed material can be recycled to the reaction zone. Ifdesired, the catalyst can be destroyed by treatment with suitabledeactivating agents such as water or alcohol, prior to the separation ofthe products.

In accordance with this invention conjugated dienes can also beoligomerized employing Ni₂ (μ-PPh₂)₂ (PEt₃)₃. Any suitable conjugateddiene or mixture of suitable conjugated dienes can be oligomerized bythe process. Generally the oligomerization employs at least oneconjugated diene having from 4 to 8 carbon atoms per molecule. Examplesof such dienes include 1,3-butadiene, 2,3-dimethylbutadiene, isoprene,piperylene, 1,3-heptadiene, 2,4-heptadiene, 1,3-hexadiene,2,3-dimethylpiperylene, and the like, and mixtures of any two or morethereof. The process involves contacting said at least one conjugateddiene with a catalyzing amount of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ in a suitablediluent under reaction conditions conducive to oligomerization.Generally the temperature of oligomerization is in the range of fromabout 100° to about 175° C, preferably in the range of about 115° toabout 150° C. The reaction is carried out with the diluent in the liquidphase. The pressure is generally in the range of about 0 to about 2000psig, preferably about 20 to about 50 psig.

Any suitable diluent can be employed that does not interfere with theoligomerization. Examples of suitable diluents include alkanes, forexample, hexane, heptane and octane; cycloalkanes, for example,cyclohexane and methylcyclohexane; aromatic hydrocarbons, for example,benzene and toluene; unsubstituted ethers, for example, diethyl ether,p-dioxane, and tetrahydrofuran; cyclic polyenes, for example,cyclooctadiene and cyclododecatriene; and mixtures of any two or morethereof. Generally the time for the reaction is in the range of about0.5 to about 6 hours, preferably about 1 to about 3 hours.

Without further elaboration, one skilled in the art using the precedingdisclosure should be able to utilize the present invention to itsfullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the specification and claims in any way whatsoever.

Unless it is indicated as otherwise the work described in the followingexamples was done at atomspheric pressure in a recirculating-atmospheredrybox providing an argon atmosphere.

EXAMPLE I Preparation ofTris(triethylphosphine)(triphenylphosphine)nickel(O) from Ni(PEt₃)₄

The tris(triethylphosphine)(triphenylphosphine)nickel(O), represented bythe formula Ni(PEt₃)₃ (PPh₃), was prepared by the following procedure: A5 ml solution of 0.52 g (2.0 mmols) of triphenylphosphine in ether wasslowly added to 0.83 g (1.6 mmols) oftetrakis(triethylphosphine)nickel(O), represented by the formulaNi(PEt₃)₄, in 5 ml of ether at 25° C. On standing, 0.19 g of orange-redcrystalline tris(triethylphosphine)(triphenylphosphine)nickel(O)precipitated. These crystals were removed by suction filtration, washedwith ether and dried in vacuo. Concentration of the filtrate underreduced pressure and cooling to -30° C resulted in an additional 0.78 gof orange-red crystals to give a total yield of 0.97 g (90% of theory);m.p. 95.5°-97° C; ir (Nujol) 2900 vs, 1585 w, 1450 s, 1425 m, 1405 w,1375 m, 1260 w, 1240 w, 1220 vw, 1080 w, 1040 w, 1030 m, 1000 vw, 985vw, 965 vw, 757 m, 743 s, 717 m, 695 s cm⁻¹ ; NMR (C₆ D₆) δ 7.7 (v br,6), 7.15 (m, >9 due to CD₅ H impurity), 1.58 (q, 18, J = 6.8 Hz), 1.05(t, 27, J = 6.8 Hz). Anal. Calcd. for C₃₆ H₆₀ NiP₄ : C, 64.01; H, 8.95;Ni, 8.69; P, 18,35. Found: C, 63.89; H, 9.28; Ni, 8.83; P, 18.37.

EXAMPLE II Preparation of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ from Ni(PEt₃)₃ (PPh₃)

A closed vial containing 1.36 g (2.0 mmol) oftris(triethylphosphine)(triphenylphosphine)nickel(O), having the formulaNi(PEt₃)₃ (PPh₃), in 20 ml of hexane was suspended in a refluxingbenzene bath. In less than about 10 minutes the orange colored solutionhad turned dark green. After 5 hours the solution was cooled to -78° Cand lustrous dark green crystals precipitated. The crystals were removedby suction filtration, washed with cold hexane, and dried in a stream ofargon to yield 0.39 g (0.46 mmol) of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ ; m.p.193°-195° C (dec.); ir (Nujol) 3040 w, 2910 vs, 2880 vs, 1580 m, 1455 s,1425 m, 1375 m, 1150 w, 1075 w, 1055 w, 1030 s, 1000 w, 767 s, 763 s,748 ms, 736 s, 724 m, 707 s, 700 vs, 694 s cm⁻¹ ; NMR (C₅ D₆) δ 7.9 (vbr, 6.6), 7.15 (v br, 17.4 - includes C₆ D₅ H impurity), 1.00 (v br,45).

Anal. Calcd. for C₄₂ H₆₅ Ni₂ P₅ : C, 59.89; H, 7.78; Ni, 13.94. Found:C, 59.54; H, 7.78; Ni, 13.88.

EXAMPLE III Preparation of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ from C₆ F₅ PPh₂ andNi(PEt₃)₄

A solution of 1.06 g (2.0 mmols) oftetrakis(triethylphosphine)nickel(O), represented by the formulaNi(PEt₃)₄, in 5 ml of ether was treated with 0.70 g (2.0 mmols) ofpentafluorophenyldiphenylphosphine, represented by the formula C₆ F₅PPh₂, in 5 ml of ether at about 0° C. The mixture turned brown and waswarmed to 25° C for 5-10 minutes before cooling to -78° C. The solutionwas then green but no crystals had formed and the mixture was evaporatedto dryness under reduced pressure to yield a dark green gum. Thisresidue was extracted with hexane, and the extract was chromatographedon a column of neutral alumina. A green colored product was eluted fromthe column with 5% ether in hexane and purification of this material byrecrystallization from hexane at -72° C gave 0.07 g (8% of theory) ofNi₂ (μ-PPh₂)₂ (PEt₃)₃. The product of this run melted at 189°-190° C(dec.) and exhibited an infrared (ir) spectrum identical to that of theproduct isolated in Example II.

EXAMPLE IV Preparation of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ from NiCl.sub. 2 (PEt₃)₂and LiPPh₂.Et₂ O

A 25 ml ether soluton containing 1.83 g (5.0 mmols) oftrans-dichlorobis(triethylphosphine)nickel(II), represented by theformula NiCl₂ (PEt₃)₂, was treated with 2.66 g (10.0 mmols) of lithiumdiphenylphosphide etherate, represented by the formula LiPPh₂.Et.sub. 2O, in 30 ml of ether at about 0° C. The solution immediately turned darkgreen. After 15 minutes 2.66 g (5.0 mmols) oftetrakis(triethylphosphine)nickel(O), Ni(PEt₃)₄, was added to thestirred solution and the mixture was allowed to stand at 25° C for 1hour before evaporating the solution to dryness under reduced pressure.The residue was extracted with about 200 ml of hexane and the extractwas filtered before chilling to -72° C. The precipitated dark greencrystals of Ni₂ (μ-PPh₂)₂ (PEt₃)₃ were removed by suction filtration,washed with hexane and dried in vacuo to give 1.54 g of product meltingat 194° C (dec.). Four additional crops of green crystals were obtainedfrom the above filtrate to increase the yield to 2.86 g (68% of theory).

A final recrystallization of the total product sample from ether at -30°C gave 1.95 g of green crystals melting at 194°-195° C (dec.). Anadditional 0.34 g of product was obtained from the filtrate. Theinfrared spectrum (Nujol) was identical to that exhibited by the Ni₂(μ-PPh₂)₂ (PEt₃)₃ product obtained in Example II.

EXAMPLE V Monoolefin Oligomerization Employing Ni₂ (μ-PPh₂)₂ (PEt₃)₃

A predried none ounce beverage bottle equipped with a magnetic stirringbar was charged in a dry box with 0.04 g (0.05 mmol) of Ni₂ (μ-PPh₂)₂(PEt₃)₃, 20 ml of chlorobenzene and then capped. The capped bottle wasremoved from the dry box and flushed successively for 1 hour periods,with argon and propylene before chilling the stirred solution for 5minutes in an ice-salt-water bath. The chilled bottle was pressured to30 psig with propylene and then vented to 5 psig. A 0.70 ml (equivalentto 0.70 mmol methylaluminum sesquichloride) aliquot of a 1 molarsolution of methylaluminum sesquichloride in chlorobenzene was added bysyringe and the solution immediately turned from green to brown. Thepressure was increased to 30 psig with propylene and maintained at thispressure in the cold bath and 1 hour later the propylene was shut off,the bottle vented and 10 ml of saturated aqueous sodium chloridesolution was added. The aqueous phase was separated, extracted with 5 mlof chlorobenzene and the chlorobenzene extract was combined with thechlorobenzene phase from the reaction mixture. The combinedchlorobenzene phases were dried over anhydrous magnesium sulfate,filtered and distilled to recover 43.4 g of propylene dimers collectedover the temperature range of 60°-68° C.

Skeletal characterization of the propylene dimers was carried out byhydrogenating a 2.0 g sample of the above isolated propylene dimers over0.1 g of platinum oxides under 50-90 psig of hydrogen for a period of 3hours. The hydrogenated product mixture was analyzed by gas-liquidpartition chromatography on a 20 ft. by 0.125 in. isoquinoline column ata 25° C oven temperature. The composition in area percent of thehydrogenated product was as follows: 19% 2,3-dimethylbutane, 68%2-methylpentane and 13% n-hexane.

EXAMPLE VI Diene Oligomerization Employing Ni₂ (μ-PPh₂)₂ (PEt₃)₃

A Predried six ounce aerosol compatibility bottle equipped with amagnetic stirring bar was charged in a dry box with 0.17 g (0.20 mmol)of Ni₂ (μ-PPh₂)₂ (PEt₃)₃, 10 ml of benzene and then capped. The cappedbottle was removed from the dry box and 20.65 g (0.382 mol) of1,3-butadiene was added. The bottle was heated in an oil bath as thecontents were magnetically stirred. The temperature was graduallyincreased. After about 1 hour at a temperature opf about 80° C thepressure in the bottle was 93 psig. The absence of any observed pressuredrop was taken to indicate that no significant reaction had yetoccurred. After heating for about 30 more minutes the temperature wasabout 118° C and the pressure in the bottle about 160 psig. After onehour at this temperature, the pressure had fallen to 143 psig. Thereaction mixture was then cooled. After being allowed to set at roomtemperature over the weekend the reaction mixture was heated to about120° C. After about an hour at this temperature the pressure in thebottle had dropped from 110 psig to 20 psig. The reaction mixture wasthen cooled and an additional 19.23 g (0.356 mol) of 1,3-butadiene wasadded. The reaction mixture was then reheated to 120° C. After about 2more hours at 120° C, the pressure again decreased to about 20 psig. Thereaction mixture was then again cooled and a further 29.67 g (0.549 mol)of 1,3-butadiene was added. After heating this mixture for about 2 morehours at 120° C the pressure dropped to about 38 psig. The reaction wasthen terminated although the solution still retained its homogeneousdark green appearance. The mixture was then exposed to air to destroythe catalyst and filtered. The filtrate was distilled to afford 28.7 gof 1,5-cyclooctadiene, 5,7 g of 1,5,9-cyclododecatriene, and otherproducts.

The terms and expressions employed in this disclosure are used as termsof description and are not intended to be unduly limiting. There is nointention in the use of such terms and expressions of excluding anyequivalents of features shown and described or portions thereof.Further, it should be recognized that various modifications are possiblewithin the scope of the following claims.

What is claimed is:
 1. Bis(μ-diphenylphosphido)tris(triethylphosphine)dinickel.
 2. A process of preparing bis(μ-diphenylphosphido)tris(triethylphosphine)dinickel, a dinickel complex comprising placing tris(triethylphosphine)(triphenylphosphine)nickel(O) in a suitable diluent to form a mixture under an inert atmosphere at a pressure such that the diluent is maintained essentially in the liquid phase while said mixture is maintained at a temperature sufficient to yield said dinickel complex.
 3. A process according to claim 2 wherein the temperature is in the range of about 25° to about 175° C and the reaction time is in the range of about 0.1 to about 100 hours.
 4. A process according to claim 3 wherein the diluent is selected from at least one aliphatic hydrocarbon having 5 to 10 carbon atoms.
 5. A process according to claim 4 wherein the temperature is in the range of about 60° to 130° C.
 6. A process according to claim 5 wherein the inert atmosphere is provided by argon.
 7. A process according to claim 6 wherein the diluent is n-hexane.
 8. A process according to claim 7 wherein the bis(μ-diphenylphosphido)tris(triethylphosphine)dinickel is recovered by cooling the reaction mixture under an inert atmosphere until said dinickel complex precipitates, separating the resulting precipitate by filtration under an inert atmosphere, washing the thus-separated precipitate under an inert atmosphere under conditions which minimize the dissolving of said precipitate, and finally drying the thus-washed precipitate under an inert atmosphere.
 9. A process according to claim 2 wherein the bis(μ-diphenylphosphido)tris(triethylphosphine)dinickel is recovered by cooling the reaction mixture under an inert atmosphere until said dinickel complex precipitates, separating the precipitate by filtration under an inert atmosphere, and drying the precipitate under an inert atmosphere. 